1. Field of the Invention
The present invention relates to a digital watermark-embedding apparatus designed to embed information as digital watermarks into a target image subject to digital watermark embedment in an entered video signal, and an art related thereto.
2. Description of the Related Art
Recent digital content such as digitized audio and digitized video data is on the increase. With digital content it is easy to provide a faithful reproduction of original content. Therefore, it is an important issue to protect the copyright of the digital content. Illegally reproduced or distributed content is very difficult to differentiate from corresponding original content. This fact involves difficulties in demonstrating an evidence to assert the copyright of the content. As a result, efforts have been made to protect the copyright of digital content.
A “digital watermark” is used as one of the efforts. The digital watermark is an art of embedding data into the audio or video data without allowing users to perceive the presence of the embedded data.
A prior art digital watermark-embedding apparatus has been disclosed in published Japanese Patent Application Laid-Open No. 11-346302.
The prior art is now described in detail with reference to FIG. 9. FIG. 9 is a block diagram, illustrating the prior art digital watermark-embedding apparatus.
In FIG. 9, a category-classifying unit 904 calculates a characteristic amount for an input image, and then determines, from the calculated characteristic amount, a category under which the image falls. The category-classifying unit 904 feeds a corresponding category index to an accumulation apparatus 902.
The accumulation apparatus 902 has a digital watermark characteristic table for each of the category indexes that are provided from the category-classifying unit 904, and selects a proper characteristic table in accordance with each of the entered category indexes. The digital watermark characteristic table describes a relationship between digital watermark intensity, a degree of degradation in image quality, and an evaluation of robustness against image processing.
The accumulation apparatus 902 determines, using the selected characteristic table, the degree of degradation in image quality and the evaluation of robustness against image processing in response to the digital watermark intensity that is fed from a digital watermark intensity-calculating unit 901. The accumulation apparatus 902 feeds the determined degree of degradation in image quality and the determined evaluation of robustness against image processing to the digital watermark intensity-calculating unit 901.
The digital watermark intensity-calculating unit 901 feeds various levels of digital watermark intensity into the accumulation apparatus 902, and then determines optimum digital watermark intensity with reference to the degree of degradation in image quality and the evaluation of toughness from the accumulation apparatus 902. The digital watermark intensity-calculating unit 901 delivers the calculated optimum digital watermark intensity to a digital watermark-embedding unit 903.
The digital watermark-embedding unit 903 converts embedded data into digital watermarks, and then embeds the digital watermarks into the input image in accordance with the optimum digital watermark intensity, thereby providing a digital watermark-embedded image.